1. Field of the Invention
The present invention relates to a light source and more particularly to an art which may be advantageously applied to a light source of a liquid crystal display device which requires a planar illuminator.
2. Description of the Prior Art
A flat light source of the prior art is described into the Japanese Patent Publication No. 58-17957. As shown in FIG. 10, a light source 4B is disposed at an end face of a transparent plate 4A which is constituted using a material having a good light transmission characteristic and the one surface 4a on the observing side is formed as a smooth surface while the other surface 4b opposed to the surface 4a as a rough surface. This rough surface 4b is so constituted not only as diffusing the light emitted from the light source 4B but also reflecting such light to the smooth surface 4a. The transparent plate 4A is constituted to provide an inclined plane, wherein it becomes thinner as it departs from the light source 4B.
The prior art described utilizes, as shown in FIG. 10, a transparent plate which becomes thinner as is becomes far from the light source 4B (thickness is reduced with increase of distance x) such as a fluorescent bulb, for example, disposed at the end face of the transparent plate 4A to provide the planar illuminator in the constitutions, (a) a single fluorescent bulb is used as shown in FIG. 10 for a planar illuminator of comparatively small area and (b) a couple of fluorescent bulbs are used as shown in FIG. 11 for a planar illuminator of large area in order to obtain a large size and high luminance planar illuminator. However, such prior art has been accompanied by problems, for example, in the case of (a) a thin and light weight planar illuminator the constitution is not suitable for high luminance and large size panel, whereas in the case of (b) a high luminance and large size planar illuminator the constitution is not suitable for a thin and light weight panel.